Alignment films are arranged on an array substrate and a color filter substrate of a thin film transistor liquid crystal display (TFT-LCD) respectively, and each alignment film is provided with grooves each extending in a certain direction, so that liquid crystal molecules are aligned along the groove extension direction when no electric field is applied. Usually, a polyimide (PI) film coated and cured on a glass substrate is rubbed using a rubbing cloth wrapped onto a rubbing roller, so as to provide a surface of the PI film with the grooves each extending in a predetermined direction. Here, the PI film becomes the alignment film having alignment function.
During the manufacture of the alignment film, due to the possible defects of the rubbing cloth, e.g., an uneven thickness, a foreign matter attached onto a surface thereof or impurities introduced during a weaving and dyeing procedure, deviations (i.e., rubbing mura) may occur for the resultant grooves on the alignment film in terms of direction, shape and depth, and therefore the alignment performance will be adversely affected. Hence, after the manufacture of the alignment film, it is necessary to detect whether or not the grooves on the alignment are defective.
In the related technologies, usually the following approach is adopted to detect whether or not the grooves on the alignment film are defective. Steam is sprayed onto the surface of the alignment film on the glass substrate by a steam sprayer (usually held by an operator), so as to generate water beads on surfaces of the grooves. Then, a region of the alignment film where the steam is sprayed is irradiated by an accent lamp, and the grooves are observed by human eyes so as to determine whether or not there is a defect. To be specific, a light beam is diffused in case of transmitting through a portion of the groove where the defect is located, and in the case that the defect is a linear mura, a bright line can be observed.
After the defect of the groove has been detected, usually a scale is used to measure a position of the defect. Upon artificial conversion, an approximate position of the defect on the rubbing cloth may be found, and then a region of the rubbing cloth where the defect is located may be repaired. Next, a new rubbing process is performed and the above steam-based detection approach is used to determine whether or not the groove of the alignment film still has the defect, thereby determining whether or not the defect of the rubbing cloth has been removed.
However, during the actual application, there are the following drawbacks in the steam-based detection approach.
Firstly, in the case that the steam is sprayed onto the glass substrate and the surface of the alignment film to generate the water beads, the water beads may gradually disappear due to air flow or evaporation. In this regard, it is necessary to spray the steam continuously within a long time during the detection, and the detection efficiency is relatively low.
Secondly, the defect of the groove on the alignment film is detected artificially, so the detection efficiency is relatively low. In addition, different operators may have different detection results due to their different standards in observing.
Thirdly, the steam sprayer is held by the operator, and in the case that the glass substrate and the alignment film are each of a large size, the steam may not be sprayed onto some regions thereof. At this time, it is impossible to determine whether or not defects exist in these regions.
Fourthly, the steam sprayer is usually connected to a water tank that is heated to generate the steam. In the case that a water level in the water tank is relatively high, some water beads in the water tank may be sputtered through the steam sprayer onto the alignment film. At this time, a subsequent process will be adversely affected.
Fifthly, along with the increase in the resolution of the TFT-LCD, the grooves on the alignment film are required to be smaller and smaller. Due to the poor homogeneity of the water beads on the surfaces of the glass substrate and the alignment film as well as limitations of observation by the human eyes, it is impossible for the steam-based detection approach to meet the requirements of detection of the alignment film of the high-resolution TFT-LCD.
Moreover, the above steam-based detection approach is performed artificially, and after the defect of the groove on the alignment film has been detected, it is usually impossible to acquire the position of the defect on the rubbing cloth accurately through the artificial conversion. In this regard, the defect on the rubbing cloth may not be removed merely through a single positioning and repairing process, i.e., several positioning and repairing processes are required. In addition, in the case that the defect on the rubbing clock is not removed through several positioning and repairing processes yet, a new rubbing cloth needs to be used. As a result, a large quantity of manpower and material resources will be consumed, and utilization of the production line will be reduced.